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Questions tagged [radio-frequency]

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why does not radio waves from radio-stations interfere with each other?

I know that radiowaves from radiostations are modulated either F.M or A.M lets suppose they Are F.M and one has carrier wave frequency of 100 Hz and other 200 Hz they have F deviation of 20Hz/V . ...
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Does attenuation to RF waves increases with frequency?

I heard somewhere that RF waves at high frequency such as above 2GHz face more attenuation while passing through air, buildings and due to humidity as compared to 800Mhz and 2) Waves at 30-40GHz ...
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2answers
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How are RF Waves transmitted?

What is the mode of transmission for RF waves at 1800 MHz. Is it ground wave propagation, Line of Sight Propagation or Atmospheric reflection (from ionosphere). What are the different ways for ...
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1answer
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Why is power density of RF waves measured in m2?

Why is power density of RF waves measured in m2 or cm (Area) and not in cm3 or m3 (volume) ? I mean aren't those waves travelling (radiating) in 3D space? I am new to this topic so please pardon ...
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Electromagnetic Waves and GPS

If the global positioning system functions through radio waves, but radio waves are reflected in the ionosphere, then how do these electromagnetic waves reach the satellites?
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4answers
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What's the physics behind XKCD #2027 (time between lightning flash and radio wave burst)?

XKCD usually has solid (and often contemporary) science behind it. Lightning Difference, #2027 one says: Q: What’s that trick for telling how many miles away lightning is? A: Just count the ...
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1answer
45 views

Radio waves collision versus waves in a pond collision

Please see the attached picture: We are trying to show an image to visualize radio wave collision and interference with regards to Maritime AIS Technology. What do colliding radio waves have in ...
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6answers
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Why put a radio telescope in space instead on the Moon?

Why are we not building a space-based radio telescope? If a lunar radio telescope is hard to build, why not a space-based radio telescope? It could be an interesting tool, I presume. Thus, what could ...
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2answers
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What is the scientific explanation for radio waves bending around the Earth?

The experiment This experiment is documented in a documentary called Convex Earth. The exact location the following information is taken from starts at 14:25. High frequency directional antennas are ...
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1answer
95 views

Why radio waves can pass through walls but not infrared waves?

My physics teacher told that infrared waves are not passing through walls due to rayleigh scattering,but rayleigh scattering increases with increase in wavelength,then why radio waves are passing ...
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1answer
34 views

How do electrons in a conductor physically respond to radio waves?

If a radio wave hits a thick piece of metal, it's my understanding that the metal will for the most part reflect the wave. What I'm unclear about is how the electrons flow in a metal that's being ...
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What band of radio frequency is reflected or absorbed by human body?

We know that radio's or antennas doesn't transmit well when they are covered by a human body.I would like to know the specific frequencies human body blocks.
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114 views

Is Nylon RF transparent?

I was doing a research on which type clothes blocks the Radio frequency. Please also list the experiments which can be performed to determine such clothes/ materials.
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Transport Networks and Information Distribution Protocols

i am new in matlab and i don't have any idea about it. the professor gave us this. really i don't understand. :( arryf A , s=cosAt+cos3t define a sum of cosine waves"number of waves is the last ...
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0answers
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A shaped pulse as a sum of rectangular pulses

I have a pulse with lineshape $L(ω)=\frac{1}{π}\frac{\frac{1}{2}Γ}{((ω−ω_0)^2+(\frac{1}{2}Γ)^2)}$ in the frequency domain where $\Gamma$ is the pulse width and $\omega_0$ is the resonant frequency ...
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1answer
27 views

Why do satellite dish come in many different sizes?

Is it to do with how many photons can be absorbed in a given area? more surfaces mean more photons are absorbed but does it translate to better quality? btw can a single atom be as good as the largest ...
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4answers
111 views

Can the equation $E = h\nu$ be used not only for light, but for radio waves? (Since they are all part of the electromagnetic spectrum)

Can the equation $E = h\nu$ (or $E = hf$) be used to find the energy of the particles from the electromagnetic spectrum? I mean, for example light is part of the EM, a radio wave is also part of the ...
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0answers
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Effect of a Lorentzian pulse on a non-resonant spin particle

I'm looking into rotation of a nuclear spin particle using a pulse with a Lorentzian lineshape. If the pulse has an area of $\frac{\pi}{2}$ and the nuclear spin frequency is on resonance with the ...
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1answer
37 views

Modelling a radiofrequency pulse

I'm looking into NMR at the moment and am trying to work out a way of modelling the action of a radiofrequency pulse on nuclear spins. Specifically, if I apply a pulse to rotate the spin by $\pi/2$ I ...
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0answers
116 views

advantages or disadvantages of pulsed laser vs continuous-wave (CW) laser

What are the advantages and disadvantages of pulsed vs CW laser? Does pulsed laser have more power compared to CW laser, or it is vice versa? If I have to guess, for long distance communication, ...
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2answers
71 views

Communications: Ground wave Propagation

(I wasn't having any tag for this question(Example: Communication-Systems, Modern-physics.)) I was studying ground wave propagation, my book writes the lines about it without explaining it. I really ...
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3answers
63 views

L-band for search radars?

I'm making my way through the Linesman-related section's of Gough's Watching the Skies. Linesman was developed to counter the carcinotron jammer. The main solution was the Type 85, which had 12 ...
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2answers
1k views

Why doesn't the ${\rm H}_2$ molecule have a permanent dipole while the neutral ${\rm H}\,{\rm\small I}$ has one?

According to the National Radio Astronomy Observatory, the $21\,{\rm cm}$ line of hydrogen can be emitted by the neutral hydrogen atom due to the magnetic interaction between the spins of the proton ...
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2answers
243 views

Reflection of radio waves at an obstacle with size half wavelength

I'm following a course about communication technology and the professor said the following multiple times: "A radio/EW-wave is reflected at an obstacle which is higher/larger than than half of the ...
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2answers
114 views

(Please Explain) Clarification on extraterrestrial communication with radio waves

I just want to get some clarifications regarding the transmission and receiving of a radio waves between planets as a means of communication with aliens for story building. Is it better to transmit ...
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1answer
91 views

Why don't radio waves ruin electronics?

Out of curiosity, I estimated the voltage amplitude for typical visible light. Wikipedia says that sunlight hits the earth at about $1000 W / m^2$. The intensity of an electric field is given by $$I =...
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1answer
209 views

Does a Faraday Cage need to be sealed to block RF?

I was watching a program on shoplifting and there were things called booster bags shown, which blocked a security tag which acts as an LC resonator when put between the security towers, causes the ...
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1answer
184 views

Power losses for electromagnetic waves radiation in copper wire with high frequency current [closed]

How to calculate electric power losses to radiation of electromagnetic waves in copper wire with high-frequency current? For example, I have a copper wire with known diameter and length and I send ...
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0answers
21 views

Magnet on a piezo - Can this oscillating field give me a radio transmitter?

I can read on wikipedia that radio waves are of frequency 3kHz-3THz. I know that piezoelectric actuator can reach eg. 20 kHz. What would happen if I put a small neodymium magnet on a piezoelectric ...
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1answer
118 views

How to convert RF absorption rate (SAR) values to electric field values?

I'm currently reading a bunch of journal articles that describe biological effects of electromagnetic fields. They often refer to the field in terms of specific absorption rate (SAR) values (W/kg). ...
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1answer
43 views

If inductive reactance increases with frequency why do tesla coils have coils?

So I was reading about the special properties of radio frequencies. Specifically I read this: "In contrast, RF current can be blocked by a coil of wire, or even a single turn or bend in a wire. This ...
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2answers
3k views

Why do I need to adjust TV antenna on the roof for better video quality?

I find it a annoying and a pain to climb up to the roof and adjust the TV antenna so that I can watch my favorite TV program without distortion. I am not using satellite service which requires a dish ...
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0answers
133 views

Weird RF manipulation in electrical circuits

I have recently seen an EEVblog tear-down of a spectrum analyzer, and it contained a few odd looking bits such as this: This got me thinking, would it be possible to create an entire electrical ...
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Radio vs X-ray pulsar timing

The detection and timing of pulsars is a common goal in astronomy (eg.1, 2). Typically these observations are done in the radio. I appreciate that observations are taken in the X-ray as well, but is ...
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0answers
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calculating the power of an interfering signal?

I'm embarissingly stuck ... Lets say I have an image in the radio regime at 100 MHz. In this image, I see the sun, and another blob, of which I am certain that it comes from some interference 100 ...
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3answers
484 views

What are crystals used for in radio?

What are crystals used for in radio? I think I sort of know the answer to this but I would like a more detailed explanation. To my current understanding, piezoelectric crystals are used to modulate ...
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0answers
37 views

Why is there less scattering at high frequencies?

Scintillation causes stars to twinkle. The same effect is present in radio astronomy and leads to e.g. pulse broadening of the signal from a pulsar. To combat this pulse broadening, observations can ...
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2answers
169 views

Transmitter and receiver precision

How precise can we make a transmitter's signal and then detect signals? ... And if different parts of the spectrum have different limits.
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1answer
82 views

How do Antennas receive information?

Do wireless signals (Wifi router, radio, telephone) send their information in single "blinks" or in a continuous wave with frequency modulation or Amplitude modulation? If a radio for example needs ...
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1answer
123 views

About The foxhole radio : coil rotation times, whether capacitor's needed

I recently tried to make a DIY foxhole radio. Althogh I made it according to the manual(140times coil rotated, ground(220V), blued razor blade, pencil core and antenna(just a steel stick about 1 meter)...
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2answers
254 views

Why are only the extremely low frequencies of electromagnetic radiation able to penetrate the earth and sea?

Wikipedia classifies ELF (Extremely Low Frequency) radiation as between 3 Hz and 300 Hz, and ULF (Ultra Low Frequency) from 300 Hz to 3 kHz. Both ranges can penetrate the earth and sea. What is the ...
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1answer
112 views

Would my house's wall stop gamma rays?

I'm wondering if there is a material which is able to stop all the electromagnetic spectrum's radiations. Something able to stop every electromagnetic radiation from the ones with the lowest frequency ...
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1answer
220 views

Bistatic radar equation for moving objects

From my understanding, and correct me if I'm wrong, the bistatic radar equation assumes that the transmitter and the receiver are separated by a distance $L$, and that the transmitter and receiver are ...
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1answer
54 views

Sideband frequencies

In amplitude modulation when carrier signal and base band signals are mixed, side band frequencies are generated. Upper side band frequency is $f_c+f_m$ and lower side band frequency is $f_c-f_m$. ...
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0answers
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Why does Skywave only work for a small frequency band?

So it is often said that waves in the HF band (3-30MHz) use skywave propagation to beam signals around the curvature of the Earth. My question is why is there this narrow limit to what is able to ...
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1answer
69 views

Do we get radiowaves if the antenna is a loop or a coil?

What happens if we use an antenna which is not a straight wire, i.e a loop or a coil? do we get EMR? Now, if we do, what is the difference between this loop and the primary winding of a transformer? ...
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2answers
71 views

The need of modulation

Why is the transmitted signal modulated rather than sending the whole signal as a radio wave? Why is it necessary to modulate the wave? I do understand there are quite advantages of modulation but ...
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3answers
1k views

How can an antenna pick up thousands of frequencies at the same time?

When we turn the tuning knob of a radio set, we pick up a different station on a different wavelength, yet the (length of the) antenna is the same: we can select any frequency at any time, we focus on ...
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1answer
206 views

How feasible is it to track down source of number station radio signals ?

How is it possible and how accurate is it to track down the origin of radio signals used by number stations that emit all around the world (and, as a bonus, how much does it cost approximately) ? I'm ...
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2answers
168 views

How do radio-frequency transmission work?

Are sound frequencies (20-20,000Hz) included in radio waves? If not, how does sound get to our end (radio/receivers)? Is there some type of encoding going on inside those radio-frequency waves or ...